1. Field of the Invention
The present invention relates to a luminescence display panel for displaying a pattern such as a character, figure, sign, design, or static image, by combining a luminescence region and non-luminescence region. More particularly, it pertains to a luminescence display panel which can be used as an electric decorative illumination panel or the like.
2. Background Art
Recently, an organic electroluminescence device (hereinafter abbreviated as “organic EL device”) known as a kind of the electroluminescence device has been put into practical use as a picture element for a flat panel display of high flexibility, or as a paper-like surface light source. As disclosed in Japanese Patent Laid-Open Publication No. 2004-111158 (see, claims, sections [0006] to [0008], and FIGS. 4 and 5), a paper-like luminescence display panel has been developed. In this luminescence display panel, a non-luminescence region of a predetermined pattern, that is, a region which does not emit light when the organic EL device is electrified, is formed in an organic EL device of a larger planar dimension. A character, figure, or sign for advertisement is displayed in the panel by a combination of a luminescence region, which emits light when the organic EL device is electrified, and the non-luminescence region.
An organic EL device is a layered body basically made by layering, on a substrate, a transparent electrode, an organic luminescence part, and a rear electrode, in this order. Out of these transparent electrode and the rear electrode, the electrode from which side electroluminescence light is extracted is formed of a transparent electrode material.
When a paper-like organic EL device is manufactured, a transparent resin film is generally used as the substrate. Although an electric conductivity of the transparent electrode is relatively low, a high electric voltage tends to be applied to the transparent electrode especially in an organic EL device of a larger planar dimension. When a high voltage is applied to the transparent electrode, there is concern that the heat generated by the flowing electricity may cause a deterioration in the organic luminescence part, a deformation in the transparent resin film serving as the substrate, or a burning of the transparent resin film.
In order to avoid these problems, a luminescence device described in Japanese Patent Laid-Open Publication No. 2003-133080 (see, claims and FIG. 2) includes a plurality of metallic bus line electrodes which are disposed with a predetermined gap therebetween on a transparent electrode, so that a heat generation can be restrained when light is emitted from the device.
As disclosed in the above Japanese Patent Laid-Open Publication No. 2003-133080, a plurality of metallic bus line electrodes disposed on a transparent electrode are helpful in restraining a heat generation when light is emitted from an organic EL device. However, a light reflectance of the metallic bus line electrode is relatively high.
Thus, when a metallic bus line electrode is disposed in a luminescence region, as in the luminescence device described in the Japanese Patent Laid-Open Publication No. 2003-133080, external light reflected on the metallic bus line electrode tends to be noticeable. In a luminescence display panel for displaying a pattern for advertisement, such as a character, figure, or sign, which kind of panel is described in Japanese Patent Laid-Open Publication No. 2004-111158, reflection of external light by a metallic bus line electrode deteriorates the image quality and thus the attractive visual effect of the panel. Therefore, reflection of external light is desired to be prevented as much as possible.
Naturally, by narrowing a line-width of the metallic bus line electrode, it is possible to prevent external light reflected on the metallic bus line electrode from being observed. However, the narrower the line-width of the metallic bus line electrode is, the higher the electric resistance of the metallic bus line electrode becomes, which makes it difficult to restrain heat generation when light is emitted from an organic EL device.